Layered elastomeric connector and process for its manufacture

ABSTRACT

Provided herein are novel layered elastomeric connectors, housings therefor and methods of manufacture for the connectors which includes alternating fused layers of a dielectric elastomer and electrically conductive fibrous mats coextensive with a cross section of the conductor to provide a multiplicity of conductive pathways between two electrically conductive surfaces.

This application is a continuation of application Ser. No. 898,857 filedAug. 20, 1986, now abandoned, which is an continuation of applicationSer. No. 683,987, filed Dec. 20, 1984, now abandoned.

TECHNICAL FIELD

This invention relates to improvements in electrical interconnectors.More particularly, the invention relates to layered elastomericconnectors including alternating fixed layers of dielectric elastomerand fibrous mats electrically conductive and a housing structuretherefor.

BACKGROUND OF THE INVENTION

As a result of increasing complexity and miniaturization associated withthe electronic assembly and computer arts, the demand for moresophisticated and reliable connectors has increased. Smaller size,lighter weight packaging and an augmented necessity for reliability havevirtually rendered obsolete individually soldered connectors in manyareas of the industry. For example, printed circuit boards, digitalwatches, portable calculators, etc., have generated the need forconnectors having the ability to reliably connect a large number ofelectrically conductive traces on closer centers in a compact area. Byno means exhaustive, the following list defines certain desirablecharacteristics for a connector: low contact resistance; close contactspacing; vibration damping; providing an environmental seal; eliminationof the need for precise alignment; inherent low contact insertion force;easily modified shape and size to meet specifications; low productioncost, etc.

A new class of connectors has evolved to satisfy these characteristics.They are layered elastomeric connectors (LEC). LEC's generally arecomposed of alternating layers of dielectric elastomer and an elastomerfilled or doped with electrically conductive material such as silverparticles, graphite particles, conductive fabrics, wires, etc. Thedielectric elastomer layers are sandwiched between the conductive layersand are of sufficient thickness to insulate the conductive layers fromone another and therefore prevent the formation of electricallyconductive or leakage pathways between the conductive layers. Among themany elastomers available for use, silicon rubbers have been settledupon as providing the material properties suitable for manufacture ofLEC's.

Silicone rubbers possess a low harness, are very temperature stable,have a low compression set and reasonable chemical inertness, andlastly, are fairly easy to process and fabricate. An LEC composed ofalternating layers of a dielectric silicone rubber and a conductiveparticle filled silicone elastomer provides a connector having a largenumber of conductive pathways in a small volume for closer contactspacing which may even provide for redundant contacts for the sameelectrical traces. Due to the inherent vibration damping of theelastomer, an LEC connecting fragile components will demonstrateprotective characteristics especially against fretting corrosion andabrasion. Additionally, the compressibility of an LEC, upon compressiononto electronic traces, provides an environmental seal in the contactzones reducing harmful effects of dust and moisture.

LEC's provide the additional advantage of easy modification of bothgeometric configuration and size to meet specifications for a particularuse. This adaptability as well as the low cost of and ease ofmanufacture of LEC's, among the other aforementioned features, havegenerated an increasing demand for LEC's.

An example of an LEC providing these features is described in BritishPat. No. 2087655. Therein are disclosed a number of embodiments for anLEC having an irregular cross section which includes a series ofwhisker-like projections from two oppositely facing peripheral surfaces.The projections are composed of discrete unidirectionally aligned linearcarbon fiber or metal wire bodies imbedded in an electrically conductiveparticle-filled elastomer. A further illustration of an LEC is providedin U.S. Pat. No. 4,295,700 disclosing an LEC where the alternatingelectrically conductive layers may be composed of conductive particlefilled elastomer, woven cloth where the wood fibers are conductive butthe warp fibers are dielectric or an identical embodiment that wasdescribed in the aforementioned British Patent. Although providing manyadvantages, certain limitations as to the applicability of LEC's doexist. First, the contact resistance of a typical particle filledelastomer is fairly high. The contact resistance results from thetransmission of electrical current across the interface between thetraces and the connector and vice versa. Where contact resistancemeasures about 30 ohm/cm, the applicability of LEC's is reduced forinterconnecting high impedance, low amperage devices, e.g., liquidcrystal devices. Moreover, heat generated by the high contact resistancemay raise the temperature of the connector area sufficiently to damageeither the connector itself or the electrical elements nearby.

The aforementioned patents contain modified LEC structures employingprojections and fibers to reduce contact resistance. However, the use ofthe fibers or projecting bodies limit the geometrical configuration andapplicability of these LEC's by restricting connections along thesurfaces from which the fibers or bodies project.

A further disadvantage of known LEC's is cost. An estimate ofconventional selling prices for an LEC is approximately one dollar perinch. Where connectors are used in abundance, particularly with theadvent of flat display panels, this cost is too high. For example, an8-inch by 4-inch panel requires nearly two linear feet of connectors.Based on a projected sales price of two hundred dollars, there would bea twenty-four dollar material cost associated with the connectors alone;simply too much for the product. Thus, it is desirable from an economicperspective to develop a lower priced LEC.

SUMMARY OF THE INVENTION

Accordingly, it is an object of this invention to provide an LECpossessing the desirable characteristics associated with LEC's generallyand overcoming recognized limitations thereof.

Another object of this invention is to provide an LEC having minimalcontact spacing, requiring minimum contact insertion force, possessingvibration damping characteristics and capable of use in a myriad ofgeometric cross-sectional configurations.

It is another object of this invention to provide an LEC possessingequal and/or superior properties relative to known LEC's.

Still another object of this invention is to provide an LECdemonstrating improved characteristics including closer contact spacingfor redundant contacts, environmental sealing, reduced contactresistance and lower manufacturing cost.

These and other objects are satisfied by a layered elastomeric connectorfor connecting at least two distinct electrical paths comprising aplurality of electrically conductive fibrous may layers coextensive withthe cross section of the connector across which at least the twoelectrical conductors are connected to each other, a plurality ofdielectric elastomeric layers each disposed between two of said matlayers and separating said mat layers to prevent electrical transmissiontherebetween with said mat layers and said elastomeric layers fusedtogether to form a stratified connector.

These objects and others are further satisfied by a method formanufacturing an LEC including the steps of producing a layeredelastomeric connector for establishing electrical contact between atleast two discrete electrical conductors, including the steps ofselecting a plurality of electrically conductive fibrous mats and aplurality of sheets of a heat-bondable, electrically nonconductive,elastomer of substantially equal cross-sectional size, alternatelystacking the elastomer sheets and the fibrous mats to form a layeredarrangement, and heating the stacked sheets and mats thereby to bond thefibrous mats and the elastomer into a unitary stratified connector.

Still other objects as well as those listed above are satisfied by aconnector assembly incorporating in an LEC, a layered, resilient,compressible elastomeric connector insert comprising a plurality offlexible, electrically conductive, fibrous sheets coextensive with thecross section of the connector, a plurality of dielectric, compressible,elastomeric layers extending coextensive with the cross section of theconnector and separating each of said fibrous sheets; said elastomericsheets and said fibrous sheets forming a unitary stratified body havingelectrically conductive bodies between each of said elastomeric layers;a housing for said connector, said housing substantially encompassingsaid connector, and comprising means for compressing said connectorperpendicular to the connector cross section, first means for permittingelectrical contact between said connector and a first electricallytransmittive surface, second means for permitting electrical contactbetween said connector and a surface of a second electrical path, saidsecond means being adapted to permit at least a portion of said surfaceof a first of the electrical paths to be inserted within said housing toabut said connector, whereupon insertion of the second surface into saidhousing, said connector is further compressed and establishes electricalcontact between said connector and the surface of said second path.

The commercial availability of silicone elastomers and highly conductivegraphitic-carbon fiber paper as well as their relative ease ofincorporation into an LEC provide a less expensive and more effectivealternative to layered conductive particle filled elastomericconnectors. Graphitic-carbon fiber paper used in an LEC has a bulkresistance rivaling that of much more expensive silver filled elastomerconnectors and a lower contact resistance. If the exposed surface of thecarbon fiber paper is plated with nickel, copper, or the like, contactresistance is considerably reduced relative to graphite filledelastomers. Carbon fiber paper also enables close contact spacing, e.g.,repeating units every 10 mils thereby providing the potential for anumber of redundant contacts. The conductive fiber paper mats are alsohighly flexible and compressible thereby minimally affecting thevibration damping characteristics of the elastomer as well as avoidingdistortion within the elastomeric layers while simultaneouslymaintaining a multiplicity of electrically conductive pathways throughthe cross section of the connector. Moreover, the conductive paper iscapable of modification so as to enhance its electric conductivity byelectroplating with various metals.

In summary, the layered elastomeric connector (LEC) contemplated by thisinvention provides greatly reduced contact resistance, particularlywhere the carbon fiber paper is electroplated electroless with specificmetals, dampens oscillatory and impact forces thereby reducing contactfretting and abrasion, provides an environmental seal againstatmospheric pollution, is capable of having very closely spaced contactcenters, and is easily produced at a low manufacturing cost.

These and other advantages and objects of this invention will becomeobvious to one of ordinary skill in the art upon review of the followingpreferred embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of the alternating layers of one preferredembodiment of the invention.

FIG. 2 is a perspective view of a stratified master rod according to onepreferred embodiment.

FIG. 3 is a perspective view of an LEC according to a preferredembodiment of this invention.

FIGS. 4 to 7 schematically illustrate the manufacturing sequence forautomated production of the layered connector.

FIG. 8 is a cutaway perspective view of an LEC and its complementaryhousing contemplated by the invention.

FIG. 9 is a partial perspective view of one embodiment of the inventionas assembled.

FIGS. 10 and 11 sequentially illustrate a low insertion forceinterconnection between two surfaces bearing electrical traces ascontemplated by this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, it is an exploded view of alternatingelectrically conductive fibrous mats 10 and elastomeric sheets 12.Fibrous mats 10 are composed of a webbing of electrically conductivefibers. Preferably, mats 10 have a thickness of less than 20 mils andmore preferably approximately 5 mils or less. In the context of alayered elastomeric connector, the thinner the layers, the greater thereplication of electrical contact points. In other words, if a 2-mil matand 4-mil insulative material are used, then a contact area exists every6 mils along the length of the connector. The redundancy of electricalcontacts assists in assuring proper connection between two conductivepaths.

The ohmic resistance of the fibrous material governs its desirabilityfor use in this invention. Preferably the mats should have a resistivityof less than 0.1 ohm cm which is about 100 times better than thatexhibited by carbon-particles field, elastomer materials and approachesthe resistivity of silver filled elastomers. An example of materialmeeting the above-specified criteria is carbon fiber paper. Carbon fiberpaper provides an interlocking web of carbon fibers thereby providing acontinuous electrically conductive path along and through the paper. Therandom crossing of fibers over one another causes the paper todemonstrate markedly lower resistance than a carbon particle filledelastomer. Carbon fiber paper is also lightweight and flexible, bothdesirable features for an elastomeric connector.

To further reduce the resistance of carbon fiber paper or an alternativeelectrically conductive fibrous mat, it has been determined thatelectroplating the mat contributes markedly to conductivity. In contrastto more expensive conventional silver filled elastomer LEC's, comparableelectrical conductivity is achieved using carbon fiber paperelectroplated with less expensive metals such as tin or nickel. Itshould be noted that if silver electroplated carbon fiber paper isselected, it demonstrates outstanding electrical conductivity farsuperior to silver particle filled elastomer.

One such preferred graphitic carbon paper contemplated for use in thisinvention is Panex CFP 30-05 manufactured by Stackpole Fiber Co. ofLowell, Massachusetts. Panex CFP 30-05, composed of 8 micron diameterfilaments, is lightweight (1.73 g/cc), has a thickness of 5 mils and hasan ohmic resistivity of 0.03 ohms cm. As noted above, the electricalconductivity of this graphitized paper is considerably enhanced byelectroplating with electrically conductive metals. Such metals include,alone or in combination, nickel, copper, tin and silver and lead. Forcontinuous plating of mats 10, which in the preferred embodiment isPanex CFP 30-05, the paper is cut into 8-inch by 1-inch strips andconnected to an anode and immersed into a plating solution. The platingsolution includes salts of one or more of the aforementioned metalswhich are reduced to elemental metal on the strips by the use of theelectrical current. During electroplating, elemental metal deposits arefirst observed at the intersection of the individual fibers andsubsequently along the fibers themselves. Table 1 emphasizes the reduceddegree of volume resistivity of plated paper over that exhibited byunplated paper.

                  TABLE 1                                                         ______________________________________                                        Volume Resistivity                                                            (of conduction layers in a layered elastomeric connector made by              electroplating on carbon filled paper)                                        ______________________________________                                        Carbon Fiber Paper                                                                             0.8 ohm cm (CONTROL)                                         Copper-Plated    0.1 ohm cm                                                   Nickel-Plated    0.4 ohm cm                                                   Tin-Plated       0.07 ohm cm                                                  Silver-Plated    0.01 ohm cm                                                  ______________________________________                                    

In order to achieve measurable reductions, the thickness of the metalplating need only be minimal. The thicker of the metal deposits or thepaper fibers, the greater the reduction. However, if the metal platingis too thick, above the 250 microinch range, the fibers become rigidwhich for the purpose of this invention is undesirable due to thecorresponding reduction in flexibility.

One preferred embodiment of the fiber paper is tin-plated Panex CFP30-05 where the volume resistance as measured to average about 0.07 ohmcm while the current carrying capacity is in the range of 1 ampere. If ahigher power circuit is involved, the tin can be substituted with silveror another highly conductive metal possessing even less resistivity thantin. Generally, however, the aforementioned characteristics oftin-plated fibers are not only acceptable but also are superior or atleast comparable to conventional silver filled elastomeric connectors orstamped metal contacts and are considerably less expensive.

The elastomer selected for use in this invention should be yielding (lowShore A hardness), resilient, and electrically insulative. Any number oforganic and inorganic materials such as polyester urethanes, styrenebutadene elastomers, copolyester-ether elastomers, exhibit theseproperties. However, due to their availability, silicon rubbers arecontemplated for use in the preferred embodiment.

In one of the preferred embodiments for making test samples, 200 gramsof Dow Corning Silastic GP-45, a translucent, dielectric, siliconerubber was compounded with 2.4 grams of Cadox TS-50, a vulcanizing agentwhich enhances the resiliency of the elastomer, on a two-roll mill atroom temperature. Fifty grams of the resulting milled composition werespread out in the cavity of a 10-inch by 12-inch plaque molded andpartially cured at 171 degrees Celsius (340 degrees Fahrenheit) for 10minutes. It was determined that the use of release sheets facilitatedremoval of the partially cured plaques from the mold. Therefore, twoTEFLON glass sheets were placed in the cavity prior to introduction ofthe elastomeric composition.

Although these curing conditions do not conform with the manufacturer'srecommendations, the properties of the resulting elastomer are desirablefor the intended purpose of the invention. The elastomer has a hardnessof 45A (Shore A durometer), a compression set of 23 percent and anelongation of 570 percent. When removed, the relatively thin elastomerfilms (10-mil) are cut into one-inch squares with a paper cutter.

The following technique was employed to generate an LEC from alternatinglayers of elastomer and fibrous conductive paper.

Metal-plated Panex paper strips are immersed into a bath of Laur 201silicone rubber dispersion. Laur 201, a primer used to bond carbon fiberpaper 10 to cured Silastic GP-45 sheets 12, is available from LaurSilicone Rubber Compounding, Inc. of Beaverton, Mich. The dispersioncontains a thermally activated cross-linking promoter and is 20 percentsolid dispersed in a 1, 1, 1 trichloroethane mixture. After the paper issaturated with the primer, it is removed from the bath and allowed todrain. The strips are then suspended in an oven for 10 to 15 minutes at100 degrees Celsius to activate the cross-linking promoter therebypartially curing the primer which forms a smooth, tough, grey-coloredcoating on the exterior surfaces of the paper. Upon removal from theoven, the dry and tack free strips are cut into one-inch squares and areready for assembly.

An improvement to Laur 201 primer is the use of a silicon-based,amino-functional, coupling agent to improve penetration of and bondingof the silicon elastomer to the carbon fibers. For example, DowCorning's Z6020, a one-percent N-β-amoethyl-γ-amino propyltrimethoxysilone solution from water or isopropanol was found toadequately induce bonding. Other possible candidates for bonding agentsinclude a titanate coupling compound of the type available from KenrichPetrochemicals, Inc. of Bayonne, New Jersey, such as LICA-38.

Assembly of the individual layers into a layered configuration isaccomplished by stacking alternating squares of elastomer and fiberpaper, one on top of the other, until a desired length is achieved. Thelayers are clamped together with minimum pressure at the upper and lowerends by a C-clamp. The stacked material is placed in an oven at 200degrees Celsius for 15 to 20 minutes. At the elevated temperature, theinterfacing primer and elastomer combine and cure thereby securelybonding the alternating layers into a single, solid, stratifiedstructure. FIG. 2 illustrates stratified master rod 14 which is composedof alternating one-inch squares of Panex fiber paper 10 and Silasticelastomer 12 bonded together. Master rod 14 is then cut to a desiredthickness and length.

The use of master rod 14 and subsequent cutting thereof assures productuniformity and reduces production costs by avoiding the need to buildand cure each individual component. Precise and easily adjustedthickness of the sliced portion from master rod 14 is achieved byholding master rod 14 under slight compression and cutting with a sharp,single-side-beveled cutting blade mounted on a milling machine.Single-sided-beveling of the cutting blade has been noted to produce aclean cut and facilitates separation and removal by peeling of thesliced section from master rod 14. Each of the slices are then cut to adesired length in the cross-sectional plane of master rod 14. Asillustrated in FIG. 2, where rod 14 is cut along lines 15A and 15Baccording to this technique, the result is four essentially identical,quarter-inch square, layered elastomeric connectors 16 depicted in FIG.3.

An alternative process for formulating the above-described conductivefiber mat based LEC is to forego the need of layered dielectricelastomer sheets 12 (spacers). Strips of Panex fiber paper are coatedwith a silicone resin by immersion into a bath of liquid silicone rubber(LSR). Dow Corning Silicone Rubber 595 diluted with toluene to reducethe viscosity of the bath was found satisfactory for this purpose.Liquid silicone rubbers are characterized as a 2 part system including afast-acting noble metal (platinum) catalyzed rubber. Thus, the need forperoxide curing agents is eliminated.

Once coated, the strips are withdrawn between two threaded bolts whichact as doctor blades to insure a uniform coating on both surfaces of thestrip. Once withdrawn, the strips are dried in an oven for fifteenminutes at 100 degrees Celsius and cut into one-inch squares. In thesame manner described above, the elastomer coated fiber paper isstacked, clamped and cured at 200 degrees Celsius in an oven forapproximately a half an hour. Like the connector described above, thisprocess produces a unitary fused connector. This second method provesadvantageous when a large number of redundant contacts is preferredbecause the method eliminates the need for the thicker elastomericsheets. Thus, the contact spacing, the separation of the conductivefibers, is reduced and the efficiency of the connector enhanced.

FIGS. 4 to 7 sequentially illustrate a manufacturing system forproduction of connector 16. Spool 50 secures a roll of 18-inch widepolyester film carrier sheet 52 (e.g., MYLAR). As sheet 52 is unrolled,it passes under feed chamber 54 containing a LSR 55 (described above).Although Dow Corning's LSR 595 is preferred, other two-part LSR's can beused such as, for example, Dow Corning's 591. The two parts arepreferably mixed in equal parts ensuring not to entrain air when placedin feed chamber 54. Roller 56 supports sheet 52 bearing liquid LSR onits upper surface which passes under doctor blade 58 thereby controllingthe thickness and producing a 3-mil layer of LSR. Carrier sheet 52 thenmoves into oven 60 at 300 degrees Fahrenheit (148 degrees Celsius) whichcures LSR 55. Passing from oven 60, carrier sheet 52 bearing the curedLSR layer moves toward take-up spool 66. Adjunct spool 64 bears a rollof slip sheet 62 (polyethylene) which is interlayered with rolledsheeting 68 on take-up spool 66. Slip sheet 62 facilitates subsequentunrolling of sheeting 68.

The next undertaking involves unrolling sheeting 68 on supply roller 70.Slip sheet 62 take up roller 72 removes interlayered slip sheet 62 fromthe upper surface of the carrier sheet. A second layer of LSR 55 iscoated on the first in the same manner as the first, with the provisothat it is 6 mils thick. Graphitized carbon paper 76 having a thicknessof 5 mils is unwound from adjunct source spool 74 and pressed into theliquid LSR layer by nippers 78 in a manner that the lower surface ofpaper 76 is impregnated and the upper surface is exposed. Carrier sheet52 moves the laminated materials into over 60 set at 176 degrees Celsius(330 degrees Fahrenheit) which leads to complete curing and bonding ofLSR coatings together. A slip sheet 62 feed and interlayering processesis employed upon take-up of laminated sheeting 80. The above-describeddual lamination technique ensures that paper 76 will not fully penetratethrough LSR 55 when it is pressed into the second layer.

In FIG. 6 is illustrated the supplementary primer coating step forlaminated sheet 80. Interlayered slip sheet 62 is removed and laminatedsheet 80 is coated with Laur 201, a preferred primer due to its lowviscosity and ease of penetration of laminated sheet 80. The solvent isremoved from the primer by air, vacuum evaporation or warming in over 60at approximately 93 degrees Celsius (200 degrees Fahrenheit). Primed,laminated composite sheet 84 is wound up on take-up roll 66 and againinterlayered with slip sheet 62. It is preferred, at this point, thatsheet 84 be slit into 11/4-inch wide tapes 86.

Tape 86 is then processed into a laminated connector employing thefollowing apparatus and procedure: Interlayered tape 86 is loaded intospool 88 from which adjunct spool 92 takes up slip sheet 64 after itpasses around roller 90. Carrier sheet 52 is removed from laminatedcomposite layer 86, passing around a roller at 94 and onto take-up spool51. Tape 82 then passes into slack tower 96 over roller 98 under tensionroller 100 attached to spring assembly 104 and then over exit roller102. Following exit from slack tower 96, tape 86 passes through tensionnipper rollers 106 and into stamping press 110 comprising reciprocatingstamper 112 and one-inch square aperture containing base frame member114. Stamper 112 impacts on tape 86 cutting it into one-inch squares116. The transport of the tape 26 into the stamping press 110 issynchronized with the stroke of the press 112, preferably by an electricstepper motor although other methods can be used. The remaining portionsof tape 86 pass through tensioning nipper rollers 108 and is collectedon take-up roller 109. Meanwhile, squares 116 collect in one-inch squaretube 120 and are compressed therein by the repeating piston action ofreciprocating stamper 112. Tube 120 passes through 148 degrees Celsius(300 degrees Fahrenheit) over 122 where the primer is activated andcements composite squares 116 together into a stratified unitary rods124 which exit from the end of tube 116. Rods 124 are then cut andprocessed in much the same manner as master rod 14 described above.

FIG. 8 schematically represents layered connector 16 and itscomplementary connecting housing 18. Housing 18 is constructed of athermoplastic material such as polyethylene nylon, polybutyleneterephthalate so that it possesses shape stability and requisitestrength for a connector housing. Housing 18 provides a configurationselected to assure adequate contact between connector 16 and anotherarticle such as a circuit board.

Housing 18 is a six-sided, elongated, rectangular container includingupper elongated slot 20, lower elongated slot 22, bore hole 24, andcavity 26. Cavity 26 extends virtually the entire length, excepting theend walls, of housing 18. Upper elongated slot 20 and lower elongatedslot 22 are substantially the same length as cavity 26. Upper slot 20runs parallel to and is contiguous with exterior wall 28. The remainingupper surface, forming upper wall 21, is of a width nearly equal to thatof connector 16. Lower slot 22 is centrally disposed along the elongatedaxis of the lower wall of housing 18. Therefore, slots 20 and 22 do notlie within the same vertical plane within housing 18. The importance ofoffsetting slots 20 and 22 will become apparent below. Wall 28 featuresinterior ridge 29 which extends the entire length of cavity 26. Ridge 29protrudes from wall 28 within cavity 26 facing connector 16.

More clearly illustrated in FIG. 9, connector 16 is lodged within cavity26. The length of connector 16 is substantially equal to that of cavity26 but the height of cavity 26 is slightly less than the width ofconnector 16, therefore, requiring connector 16 to be slightlycompressed when seated within cavity 26. Due to the slight compressionrequired to seat connector 16 within housing 18 and the elastomericnature of connector 16, some displacement occurs therein. Moreparticularly, the compression of connector 16 causes it to bulge withinlower slot 22 and protrude into the space facing ridge 29. Accordingly,when properly seating within housing 18, connector 16 is not perfectlyrectangular but is displaced in two directions; into lower slot 22 andtoward ridge 29.

FIGS. 10 and 11 pictorially represent the means by which electricalcontact is established by use of this invention. Housing 18, containingconnector 16, is attached to circuit board 40 by way of screw 30, whichpasses through hole 24 in housing 18 and through a complementary holeprovided in board 40. Screw 30 secures container 18 to board 40 with nut31. Connector 16 is in a light contact position with electricallytransmittive features 41 located on the upper surface of board 40 asillustrated in FIG. 10. A second board 42, containing electricallytransmittive features 43 along one surface is inserted through slot 20and to the base of cavity 26 so that features 43 contact connector 16.As clearly represented in FIG. 11, the insertion of board 42 into cavity26, generates compressive force which further distorts elastomericconnector 16 causing greater expansion into slot 22. It can beappreciated that the further expansion of connector 16 into slot 22increases the contact surface area and, therefore, creates a moresubstantial contact between connector 16 and transmittive surface 41.Furthermore, by this arrangement, the contact area between connector 16and surface 41 is environmentally sealed from the atmosphere. Ridge 29provides a spacer between the back of board 42 and wall 28 therebycausing even greater compressive force on elastomeric connector 16 whichin turn assures substantial and complete contact as well as anenvironmental seal between connector 16 and transmittive surface 43.

The contact established between connector 16 and transmittive surface 43is established by the frictional engagement generated by sliding board42 along connector 16 in cavity 26. The rubbing, more commonly referredto as wiping contact, describes the contact between electricallyconductive fibers forming connector 16 and transmittive surface 43. Thewiping contact serves not only to wipe oxidation, etc. from thetransmittive elements 43 but also to seal the final contact positionfrom deleterious atmospheric elements. Moreover, the contact resistivityis reduced between electrically transmittive surfaces 41 and 43 andlayers 10.

Because connector 16 and cavity 26 are of substantially identicallength, the compressive nature of the seating of connector 16 withinhousing 18, distorts connector 16 in only the vertical (cross-sectional)plane. This vertical distortion, in contrast to anisotropic displacementmaintains alternating layers 10 and 12 in parallel, verticalrelationship thereby assuring matching contact in the vertical planebetween surface 43 and surface 51. Accordingly, a single transmittiveelement 41 will be satisfactorily connected to its correspondingtransmittive element 43 through conductive connector layers 10. Indeed,the particular arrangement contemplated by this invention is intended toprovide redundant contact surfaces, i.e., a plurality of connectorfibrous conductive layers 10 corresponding to each transmittive element41 and corresponding element 43 on boards 40 and 42, respectively.

To assess uniformity and assure quality control, testing and evaluationprocedures have been established for LEC 16. The connector resistance ismeasured by clamping LEC 16 between two gold-plated electrodes. Theelectrodes are connected to a 100-milligram constant current powersupply such as that manufactured by Hewlett Packard. At constantcurrent, measuring the voltage drop with a voltmeter between theelectrodes permits calculation of the resistivity. The volumeresistivity (ρ) of each conductive fiber layer may also be determined bymultiplying the calculated resistance (R) by the cross-sectional area ofthe LEC and then dividing the result by the conductive path length(CPL). The volume resistivity of LEC may vary due to the number ofconductive traces contained (number of conductive layers per length).Therefore, it is desirable to determine comparative resistivity ratherthan an absolute measurement. The following formula may be used for thispurpose so long as the assumption that each conductive layer is ofequivalent resistivity: ##EQU1## where ρ=volume resistivity

R=calculated resistance (determined by voltage drop)

A=averaged over number of conductive layers

N=number of conductive layers

W=width of conductive layers

H=height of conductive layers

CPL=conductive path length

The following sample calculation is provided to illustrate the use ofthe formula:

Given:

R=0.077 ohms (as calculated)

N=17 (number of elements)

W=1.27×10⁻² cm

H=0.7 cm

CPL=0.2 cm

Assume:

    R.sub.1 =R.sub.17

where (1/R)=(1/R1)+(1/R2) . . . (1/R17)

Therefore:

    R=(R.sub.N /17)

RN=17R (17×0.077)=1.31 ohms

and; ##EQU2## ρ element=0.065 ohm cm

The above-described preferred embodiments are intended to beillustrative, not limitive. For example, a rectangular connector isdescribed. However, it is appreciated that the above-describedconnectors may have cross sections of many geometries; cylindricalC-shaped, T-shaped, as well as other irregular configurations desiredfor a particular purpose.

Other such variations and modifications of the invention should now beobvious to the skilled artisan and are intended to fall within thespirit and scope of the invention as defined by the following claims:

I claim:
 1. An electrical connector for electrically connectingconductive areas of first and second members comprising an elongatedmember which defines a length axis and a cross sectional surface thatextends between the first and second member, said elongated membercomprising:a plurality of electrically conductive fibrous mat layers,each of said mat layers coextensive with said cross sectional surfaceeach mat layer having randomly positioned fibers which are in electricalengagement with each other; a plurality of dielectric elastomericlayers, each disposed between a respective adjacent pair of said matlayers such that the elastomeric layers separate said mat layers andprevent electrical transmission therebetween and adjacent pairs of saidmat layers are aligned along the length axis, said mat layers and saidelastomeric layers adhered together to form said elongated member;whereby the conductive fibrous mat layers of the electrical connectorhave enhanced conducting characteristics due to the low resistance ofthe fibers of the fibrous mat layers, and the dielectric elastomericlayers, as well as the conductive fibrous mat layers, have the resilientcharacteristics to insure that a positive electrical connection iseffected between the conductive areas of the first and the secondmembers.
 2. An electrical connector as claimed in claim 1, characterizedin that the fibers forming said mat layers are plated with anelectrically-conductive metal.
 3. An electrical connector as claimed inclaim 1, characterized in that the fibers forming said mat layers are ofgraphite carbon.
 4. An electrical connector as claimed in claim 1,characterized in that the mat layers are flexible.
 5. An electricalconnector as claimed in claim 1, characterized in that said elastomericlayers are bonded to the mat layers by the elastomeric material of theelastomeric layers.
 6. An electrical connector as claimed in claim 1,characterized in that a coupling agent promotes bonding between theconductive fibrous mat layers and the elastomeric layers, the couplingagent being selected from the group of a silicone rubber dispersion, anamino-silicon functional coupling agent such as N- -amoethyl- -aminopropyl trimethoxysilone or a titanate coupling agent.
 7. An electricalconnector as claimed in claim 1, characterized in that said elastomericlayers comprise a silicone rubber.
 8. An electrical connector as claimedin claim 1, characterized in that said elastomeric layers comprise avulcanized silicone rubber.
 9. An electrical connector as claimed inclaim 1, characterized in that a housing member has a space in whichsaid elongated member is disposed, said housing member is mountable ontoa first circuit board having conductive members, a first opening islocated in said housing member through which part of said elongatedmember extends so that the conductive fibers of said fibrous mat layerselectrically engage the conductive members, and a second opening islocated in said housing member through which an end of a second circuitboard having conductive members passes so that the conductive membersare electrically engageable with the conductive fibers of the fibrousmat layers.
 10. The electrical connector as claimed in claim 1 whereinsaid cross sectional surface extends completely across the elongatedmember.
 11. The electrical connector as claimed in claim 1 wherein eachof said mat layers comprises a respective conductive fiber paper sheet.12. The electrical connector as claimed in claim 1 wherein each of saidmat layers comprises a respective carbon paper sheet.
 13. The electricalconnector as claimed in claim 1 wherein each of said mat layers isshaped as a thin sheet having a smallest dimension aligned with theaxis.
 14. An electrical connector for electrically connecting conductiveareas of first and second members, comprising:layers of dielectricelastomeric material and conductive members being in the form of sheetsof a fabric of conductive fibers wherein the fibers are randomlypositioned in electrical engagement with each other to form the fabric,said elastomeric material being in the form of elastomeric sheets, saidsheets of fabric of conductive fibers being disposed between saidelastomeric material and conductive areas for electrical connection withthe conductive areas of the first and second members; whereby the sheetsof conductive fibers of the electrical connector have enhancedconductive characteristics due to the low resistance of the fibers, andthe layers of dielectric elastomeric material, as well as the sheets ofconductive fibers, have the resilient characteristics required to insurethat a positive electrical connection is effected between the conductiveareas of the first and the second members.
 15. An electrical connectoras claimed in claim 14 wherein the fabric of conductive fibers comprisescarbon fiber paper.
 16. An electrical connector for electricallyconnecting conductive areas of first and second members comprising anelongated member formed of dielectric elastomeric material andconductive members, characterized in that:said conductive members are inthe form of a conductive fibrous mat layer having randomly positionedfibers which are in electrical engagement with each other and saiddielectric elastomeric material is in the form of an elastomeric sheet,said fibrous mat layer being disposed between elastomeric sheets, andsaid fibrous mat layers and said elastomeric sheets being adheredtogether forming the elongated member; a housing member has a space inwhich said elongated member is disposed, said housing member ismountable onto a first circuit board having conductive members, a firstopening is located in said housing member through which part of saidelongated member extends so that the conductive fibers of said fibrousmat layers electrically engage the conductive members, and a secondopening is located in said housing member through which an end of asecond circuit board having conductive members passes so that theconductive members are electrically engageable with the conductivefibers of the fibrous mat layers; said housing member has an arcuatesection on an inside surface thereof which urges the end of the secondcircuit board into engagement with the elongated member.
 17. Anelectrical connector for electrically connecting conductive areas offirst and second members, comprising:a stack of insulating members andconductive members bonded together to form a continuous connector memberhaving a uniform cross section along an axis, said insulating membersalternating with said conductive along said axis such that saidinsulating members separate and electrically insulate adjacent pairs ofsaid conducting members, said insulating members and said conductivemembers each shaped to correspond said uniform cross section; each ofsaid insulating members comprising a respective elastomeric layer; eachof said conductive members comprising a respective self-supportingfibrous mat layer comprising randomly positioned conductive fibers whichprovide low resistance electrical interconnections and which areessentially free to move with respect to each other when a compressiveforce is applied thereto; whereby said conductive members have enhancedconductive characteristics due to the low resistance of the conductivemembers, and said insulating members, as well as said conductivemembers, have the resilient characteristics to insure that a positiveelectrical connector is effected between the conductive areas of thefirst and the second members.
 18. An electrical connector as claimed inclaim 17 wherein each of said mat layers comprises a respectiveconductive fiber paper sheet.
 19. An electrical connector as claimed inclaim 17 wherein each of said mat layers comprises a respective carbonpaper sheet.
 20. An electrical connector as claimed in claim 17 whereineach of said mat layers is shaped as a thin sheet having a smallestdimension aligned with said axis.